Various techniques have been used for welding plastic tubes, particularly as used in the medical field. For example, there are situations where medical or scientific procedures require sterile transfer of dangerous or sensitive fluids from one container to another. For example, in continuous ambulatory peritoneal dialysis (CAPD) the procedure involves replacing hemo-dialysis. The CAPD patient has a tube connected to the patient's peritoneal cavity via an implanted catheter. A tube from a bag of fresh dialysis solution is connected to the patient's tube. The fresh dialysis solution is drained from the bag into the patient's peritoneal cavity where it remains for about 3-4 hours. During this treatment period the empty bag is folded and carried by the patient who can continue with his or her normal activities. After this treatment period the spent dialysate is drained back into the empty bag which is then disconnected from the patient's tube. A bag of fresh dialysis solution is then connected to the patient's tube and the procedure is repeated. In this connection process the tube from the new bag is to be welded to the tube leading from the patient so that the new bag can replace the used bag. This process involves cutting the tubes of both bags and then welding the tube from the new bag to the tube from the patient. Similar techniques which require cutting plastic tubes and then welding a portion of one tube to another tube includes such processes as blood processing, bio-medical technology labs, total parenteral feeding, chemotherapy, urinary drainage and indwelling catheters.
A common technique used for the cutting of the plastic tubes and then welding the tubes together utilizes a heated wafer which cuts through a pair of tubes either simultaneously or sequentially. The heated tube ends are in a molten condition so that by shifting the tubes a molten tube end from one of the tubes is disposed inline with a molten tube end from the other tube. The molten ends are pressed together to weld the two tube sections and form a unitary tube. U.S. Pat. Nos. 4,610,670; 4,619,642; 4,770,735; 4,793,880; 4,832,773; 4,864,101; 4,897,138; 4,913,756; 4,933,036; 5,141,592; 5,156,701; 5,158,630; 5,209,800; 5,244,522; 5,248,359; 5,256,229; 5,279,685; 5,397,425; 5,525,186; 5,632,852; 5,674,333; 5,855,731; 5,871,612; 6,020,574; 6,132,833; 6,177,652; and 6,637,489 are examples of techniques using heated wafers. All of the details of these patents are incorporated herein by reference thereto.
U.S. Pat. No. 6,913,056 discloses an apparatus and method for connecting and disconnecting flexible tubing without a heated wafer and which involves crimping a tube in guides during the disconnect procedure. A hammer located between the guides moves into contact with the tube pushing liquid out of the area to be disconnected. As the tube is pinched between the hammer and an anvil a laser heats the pinched tube to seal it. The hammer remains in contact with the tube while it cools. The hammer then moves back to its original position and the guides are removed in reverse pulling the tube apart with two sealed ends.
One of the main problems in sterile connection technology has been welding liquid filled tubes. The weld site must be clear and free of any fluid or fluid ingress before a welding process can begin. The prior art techniques for removing and preventing fluid from entering the weld site are generally characterized by intrinsic weakness or are expensive to implement. Some prior techniques involve minimizing clamping distances or registering sealed tube ends to prevent trapping fluid beyond the clamp faces. These techniques work but have a small operating window and cannot guarantee consistent fluid free weld sites. Other methods include the use of rollers or even of creating temporary seals to remove fluids from the weld site prior to completing a weld. While these systems are functional they are difficult and expensive to implement.